Progressive relaxation

Question

I need to progressively relax my query, however, what I want is as follows:
If someone searched for say "Acrylic Crochet Throws" then
- the results with exact match should come on top
- followed by the match with stemming but all three words next to each other
- then a near search with max span of 15
- after this I want to repeat the above three conditions with combination of any two words i.e. "Acrylic Crochet", "Acrylic Throws" and "Crochet Throws"
Similarly if the searched string as 4 words, then it should first search for all 4 words, then combination of 3 words, then combination of two words.
Can someone guid me on how to achieve this
Madhup

Answer 1

In the example below, I have written a user-defined function to return the sequences for the progressive query relaxation. I wrote it to handle groups of up to four words. If you want more, just add more nested loops to the function. I included examples of what the function returns. I demonstated a query with a context index and contains, so that you can see that it works by the scores. However, I recommend that you use a ctxcat index and catsearch, as in the last query. There is a bug with context and contains not returning any rows if the first criteria of progressive query relaxation is not met and the optimizer uses the domain index.
SCOTT@10gXE> -- table and data:
SCOTT@10gXE> CREATE TABLE test_tab
  2    (test_col VARCHAR2 (50))
  3  /
Table created.
SCOTT@10gXE> INSERT ALL
  2  INTO test_tab VALUES ('acrylic crochet throws')
  3  INTO test_tab VALUES ('acrylic crochets throwing')
  4  INTO test_tab VALUES ('acrylic word2 crochet word4 throws')
  5  INTO test_tab VALUES ('acrylic crochet')
  6  INTO test_tab VALUES ('acrylic throws')
  7  INTO test_tab VALUES ('crochet throws')
  8  INTO test_tab VALUES ('acrylics crocheting')
  9  INTO test_tab VALUES ('acrylics throwing')
10  INTO test_tab VALUES ('crocheting throw')
11  INTO test_tab VALUES ('acrylic word2 crochet')
12  INTO test_tab VALUES ('acrylic word2 throws')
13  INTO test_tab VALUES ('crochet word2 throws')
14  sELECT * FROM DUAL
15  /
12 rows created.
SCOTT@10gXE> -- function:
SCOTT@10gXE> CREATE OR REPLACE FUNCTION seqs
  2    (p_words        IN VARCHAR2)
  3    RETURN            VARCHAR2
  4  AS
  5    v_words            VARCHAR2 (32767) := LTRIM (RTRIM (p_words));
  6    v_result        VARCHAR2 (32767);
  7    v_spaces        INTEGER;
  8    v_string        VARCHAR2 (32767);
  9    TYPE t_varchar2 IS TABLE OF VARCHAR2(255) INDEX BY BINARY_INTEGER;
10    t_words            t_varchar2;
11  BEGIN
12    WHILE INSTR (v_words, '     ') > 0 LOOP
13        v_words := REPLACE (v_words, '  ', ' ');
14    END LOOP;
15    v_result := v_result || CHR(10) || '<seq>' || v_words || '</seq>';
16    v_result := v_result || CHR(10) || '<seq>$' || REPLACE (v_words, ' ', ' $') || '</seq>';
17    v_result := v_result || CHR(10) || '<seq>NEAR((' || REPLACE (v_words, ' ', ', ') || '), 15, TRUE)</seq>';
18    v_spaces := LENGTH (v_words) - LENGTH (REPLACE (v_words, ' ', ''));
19    IF v_spaces > 1 THEN
20        v_string := v_words || ' ';
21        FOR i IN 1 .. v_spaces + 1 LOOP
22          t_words (i) := SUBSTR (v_string, 1, INSTR (v_string, ' ') - 1);
23          v_string := SUBSTR (v_string, INSTR (v_string, ' ') + 1);
24        END LOOP;
25        FOR n IN REVERSE 1 .. v_spaces - 1 LOOP
26          FOR x IN 1 .. 3 LOOP
27            v_result := v_result || CHR(10) || '<seq>';
28            v_string := '';
29 
30            FOR i IN 0 + 1 .. GREATEST (LEAST (v_spaces + 1 - n, v_spaces + 1), 0+1)
31            LOOP
32              IF n >= 1 THEN
33             FOR j IN i + 1 .. GREATEST (LEAST (v_spaces + 2 - n, v_spaces + 1), i+1)
34             LOOP
35               IF n >= 2 THEN
36                 FOR k IN j + 1 .. GREATEST (LEAST (v_spaces + 3 - n, v_spaces + 1), j+1)
37                 LOOP
38                   IF n >= 3 THEN
39                  FOR l IN k + 1 .. GREATEST (LEAST (v_spaces + 4 - n, v_spaces + 1), k+1)
40                  LOOP
41                    v_string := v_string || t_words(i) || ' ' || t_words(j) || ' ' || t_words(k) || ' ' || t_words(l);
42                    v_string := v_string || CHR(10) || 'OR ';
43                  END LOOP;
44                   ELSE
45                  v_string := v_string || t_words(i) || ' ' || t_words(j) || ' ' || t_words(k);
46                  v_string := v_string || CHR(10) || 'OR ';
47                   END IF;
48                 END LOOP;
49               ELSE
50                 v_string := v_string || t_words(i) || ' ' || t_words(j);
51                 v_string := v_string || CHR(10) || 'OR ';
52               END IF;
53             END LOOP;
54              ELSE
55             v_string := v_string || t_words(i);
56             v_string := v_string || CHR(10) || 'OR ';
57              END IF;
58            END LOOP;
59 
60            v_string := RTRIM (RTRIM (v_string, 'OR '), CHR(10));
61            IF x = 2 THEN
62              v_string := '$' || REPLACE (v_string, ' ', ' $');
63            ELSIF x = 3 THEN
64              v_string := 'NEAR(('
65             || REPLACE (REPLACE (v_string, ' ', ','), CHR(10) || 'OR,',
66                      '), 15, TRUE)' || CHR(10) || 'OR NEAR((')
67             || '), 15, TRUE)';
68            END IF;
69            v_result := v_result || v_string;
70            v_result := v_result || '</seq>';
71          END LOOP;
72        END LOOP;
73    END IF;
74    RETURN LTRIM (v_result, CHR(10));
75  END seqs;
76  /
Function created.
SCOTT@10gXE> sHOW ERRORS
No errors.
SCOTT@10gXE> -- examples of what seqs function returns:
SCOTT@10gXE> VARIABLE g_words VARCHAR2(2000)
SCOTT@10gXE> EXEC :g_words := 'word1 word2 word3 word4'
PL/SQL procedure successfully completed.
SCOTT@10gXE> SELECT seqs (:g_words) FROM DUAL
  2  /
SEQS(:G_WORDS)
<seq>word1 word2 word3 word4</seq>
<seq>$word1 $word2 $word3 $word4</seq>
<seq>NEAR((word1, word2, word3, word4), 15, TRUE)</seq>
<seq>word1 word2 word3
OR word1 word2 word4
OR word1 word3 word4
OR word2 word3 word4</seq>
<seq>$word1 $word2 $word3
OR $word1 $word2 $word4
OR $word1 $word3 $word4
OR $word2 $word3 $word4</seq>
<seq>NEAR((word1,word2,word3), 15, TRUE)
OR NEAR((word1,word2,word4), 15, TRUE)
OR NEAR((word1,word3,word4), 15, TRUE)
OR NEAR((word2,word3,word4), 15, TRUE)</seq>
<seq>word1 word2
OR word1 word3
OR word1 word4
OR word2 word3
OR word2 word4
OR word3 word4</seq>
<seq>$word1 $word2
OR $word1 $word3
OR $word1 $word4
OR $word2 $word3
OR $word2 $word4
OR $word3 $word4</seq>
<seq>NEAR((word1,word2), 15, TRUE)
OR NEAR((word1,word3), 15, TRUE)
OR NEAR((word1,word4), 15, TRUE)
OR NEAR((word2,word3), 15, TRUE)
OR NEAR((word2,word4), 15, TRUE)
OR NEAR((word3,word4), 15, TRUE)</seq>
SCOTT@10gXE> EXEC :g_words := 'Acrylic Crochet Throws'
PL/SQL procedure successfully completed.
SCOTT@10gXE> SELECT seqs (:g_words) FROM DUAL
  2  /
SEQS(:G_WORDS)
<seq>Acrylic Crochet Throws</seq>
<seq>$Acrylic $Crochet $Throws</seq>
<seq>NEAR((Acrylic, Crochet, Throws), 15, TRUE)</seq>
<seq>Acrylic Crochet
OR Acrylic Throws
OR Crochet Throws</seq>
<seq>$Acrylic $Crochet
OR $Acrylic $Throws
OR $Crochet $Throws</seq>
<seq>NEAR((Acrylic,Crochet), 15, TRUE)
OR NEAR((Acrylic,Throws), 15, TRUE)
OR NEAR((Crochet,Throws), 15, TRUE)</seq>
SCOTT@10gXE> -- query with context index and contains
SCOTT@10gXE> -- (not recommended, just used to show score)
SCOTT@10gXE> CREATE INDEX test_idx1 ON test_tab (test_col)
  2  INDEXTYPE IS CTXSYS.CONTEXT
  3  /
Index created.
SCOTT@10gXE> SELECT test_col, score (1)
  2  FROM   test_tab
  3  WHERE  CONTAINS (test_col,
  4                   '<query>
  5                   <textquery>
  6                     <progression>'
  7                     || seqs (:g_words)
  8                     || '</progression>
  9                   </textquery>
10                 </query>',
11                   1) > 0
12  /
TEST_COL                                             SCORE(1)
acrylic crochet throws                                     84
acrylic crochets throwing                                  67
acrylic word2 crochet word4 throws                         54
acrylic crochet                                            34
acrylic throws                                             34
crochet throws                                             34
acrylics crocheting                                        17
acrylics throwing                                          17
crocheting throw                                           17
acrylic word2 crochet                                       3
acrylic word2 throws                                        3
crochet word2 throws                                        3
12 rows selected.
SCOTT@10gXE> -- query with ctxcat index and catsearch (recommended):
SCOTT@10gXE> CREATE INDEX test_idx2 ON test_tab (test_col)
  2  INDEXTYPE IS CTXSYS.CTXCAT
  3  /
Index created.
SCOTT@10gXE> SELECT test_col
  2  FROM   test_tab
  3  WHERE  CATSEARCH (test_col,
  4                   '<query>
  5                   <textquery>
  6                     <progression>'
  7                     || seqs (:g_words)
  8                     || '</progression>
  9                   </textquery>
10                 </query>',
11                   NULL) > 0
12  /
TEST_COL
acrylic crochet throws
acrylic crochets throwing
acrylic word2 crochet word4 throws
acrylic crochet
acrylic throws
crochet throws
acrylics crocheting
acrylics throwing
crocheting throw
acrylic word2 crochet
acrylic word2 throws
crochet word2 throws
12 rows selected.
SCOTT@10gXE>